This invention relates to vehicle warning apparatus and more particularly to such apparatus for indicating a low air pressure condition within a pneumatic tire while the associated vehicle is moving along a roadway.
It is very difficult to detect by "feel" the presence of a low pressure tire, especially in heavy trucks (multiple tires) or a trailing vehicle. However, it is important to be constantly aware of the tire conditions since serious accidents may result should one of the tires go flat. This is true especially of a towed vehicle that will often include only two such tires and a single connecting point between it and the towing vehicle. Further, even low tire pressure is hazardous in towed vehicles since they have a tendency to pull in the direction of the low pressure tire and therefore swerve in that direction. It is therefore desirable to obtain some means to indicate to the vehicle operator when a low pressure exists in one or more of the vehicle or towed vehicle tires.
U.S. Pat. No. 3,055,998 to S. L. Collins discloses a tire deflation indicator. Collins uses an indicator box at each vehicle wheel. Each box includes a housing that is fastened by straps to the associated vehicle axle. The housing rotatably mounts a shaft that includes a hub protruding outwardly of the housing. A feeler rod is mounted to the exposed hub for engaging the ground and turning the shaft when the adjacent tire becomes deflated. The shaft is held in a normal upright condition by a separate coil spring. An arm is fixed to the shaft within the housing to swing into engagement with an electrical switch actuator in response to pivotal movement of the feeler rod. The arm is turned when the feeler rod engages the ground. A signal device is electrically connected to the switch and is located within the vehicle to provide early warning to the operator that a tire is going flat.
U.S. Pat. No. 3,647,967 to Moot discloses a low tire indicator. It shows a contact finger on a ground engaging rod. A ball at the bottom of the rod lifts the rod and its associated hinge block up and laterally when the ball strikes the ground. This moves an upper tip of the rod against an electrical contact to complete a circuit and signals the operator of the associated vehicle of a low tire condition.
U.S. Pat. Nos. 1,947,760, 2,763,743, and 2,213,782 all relate to tire pressure warning devices that actually sense the low pressure condition. They do this by providing switch actuator arms that engage the bulging side of a tire as it begins to go flat.
U.S. Pat. No. 3,096,410 to Anderson discloses a rather complex low tire warning device. It includes a coiled spring earth contacting arm 50 which includes a switch element. This element operates another switch mechanism in a box mounted to the associated vehicle axle.
U.S. Pat. No. 3,413,593 to Uphoff shows a ground contacting feeler arm mounted to an axle adjacent a wheel. The arm bends in response to contact with the roadway surface to actuate an electrical switch. The switch is enclosed in a waterproof covering.
U.S. Pat. No. 3,072,759 to Kreps shows a trailer flat indicator. A stationary switch member and a movable switch member is mounted to a ground engaging spring arm. The lower end of the spring arm which comes into ground contact is constructed of belting. The two contacts provide an electrical ground to the trailer frame for a signal circuit when they are engaged.
The present alarm basically differs from the above described apparatus in its simplicity of design and function. It includes only one moving part, the ground engaging rod. This rod constitutes a conductor to ground a warning circuit to the vehicle axle. The rod is normally held away from contacting a simple, single piece conductor pad by an integral spring member. A rubber filler helps provide a watertight seal to the housing that encloses the conductor pad. Since the rod serves as a grounding conductor in the warning circuit, only one wire need be connected to the vehicle wiring system, on the ungrounded side of the vehicle electrical supply. The electrical contact elements are well insulated and sealed to assure proper functioning in all weather and roadway conditions.